December 14, 1990: A worker from the San Francisco Department of Public Works peers into the collapsed portion of Jones Street at Bush Street intersection. The cause of the cave in, approximately 24 feet around and ten feet deep, was under investigation. Photo courtesy of the AP. less

December 14, 1990: A worker from the San Francisco Department of Public Works peers into the collapsed portion of Jones Street at Bush Street intersection. The cause of the cave in, approximately 24 feet around ... more

December 14, 1990: A worker from the San Francisco Department of... Photo-12352954.141211 - SFGate

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May 25, 1958: Sinkhole at Post and Polk Streets in San Francisco.

May 25, 1958: Sinkhole at Post and Polk Streets in San Francisco.

Photo: Art Frisch, San Francisco Chronicle

May 25, 1958: Sinkhole at Post and Polk Streets in San Francisco. Photo-12352953.141211 - SFGate

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March 14, 1990: A leak in a broken sewer line that was caused by the October, Loma Prieta, earthquake, caused a big hole in a busy street in downtown San Francisco. The 12' x 15' wide sinkhole was located next to the now torn down Central Freeway, on the Embarcadero. Photo courtesy of AP. less

March 14, 1990: A leak in a broken sewer line that was caused by the October, Loma Prieta, earthquake, caused a big hole in a busy street in downtown San Francisco. The 12' x 15' wide sinkhole was located next ... more

March 14, 1990: A leak in a broken sewer line that was caused by... Photo-12352956.141211 - SFGate

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April 25, 1978: Sinkhole on the cable car line at Ellis and Powell Streets in San Francisco. Service had to be halted.

April 25, 1978: Sinkhole on the cable car line at Ellis and Powell Streets in San Francisco. Service had to be halted.

Photo: Stephanie Maze, San Francisco Chronicle

April 25, 1978: Sinkhole on the cable car line at Ellis and Powell... Photo-12352974.141211 - SFGate

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Taboola Gallery Frame Item-85307.141211 - SFGate

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April 22, 1957: A worker, Bernard Goodin, was trapped by a mountain of dirt at Civic Center's "Mole Hall" aka Brooks Hall, during construction of the underground structure.

April 22, 1957: A worker, Bernard Goodin, was trapped by a mountain of dirt at Civic Center's "Mole Hall" aka Brooks Hall, during construction of the underground structure.

Photo: Chronicle Archives

April 22, 1957: A worker, Bernard Goodin, was trapped by a mountain... Photo-12352977.141211 - SFGate

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November 30, 1960: A broken water main caused the street to collapse at 34th Avenue and Wawona Street in San Francisco.

November 30, 1960: A broken water main caused the street to collapse at 34th Avenue and Wawona Street in San Francisco.

Photo: Gordon Peters, San Francisco Chronicle

November 30, 1960: A broken water main caused the street to... Photo-12352982.141211 - SFGate

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October 19, 1959: The ground collapsed at the site of the construction of the Comstock Apartments, on Jones Street in San Francisco.

October 19, 1959: The ground collapsed at the site of the construction of the Comstock Apartments, on Jones Street in San Francisco.

Photo: Joe Rosenthal, San Francisco Chronicle

October 19, 1959: The ground collapsed at the site of the... Photo-12352983.141211 - SFGate

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December 14, 1990: Concrete collapsed on Jones Street at Bush Street. The photo shows city workers repairing the damage.

December 14, 1990: Concrete collapsed on Jones Street at Bush Street. The photo shows city workers repairing the damage.

July 25, 1981: A broken water main caused a 25' diameter hole, 10' deep. A sign, "Open for inspection" fell into the hole, on Judah Street in San Francisco's Sunset District.

July 25, 1981: A broken water main caused a 25' diameter hole, 10' deep. A sign, "Open for inspection" fell into the hole, on Judah Street in San Francisco's Sunset District.

Photo: John O'Hara, San Francisco Chronicle

July 25, 1981: A broken water main caused a 25' diameter hole,... Photo-12352988.141211 - SFGate

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September 21, 1974: A sand cave in San Francisco's Hunter's Point, had a cave in. Sadly, one person died and one person was hurt. Shown in the photo is Charlotte Washington, a K.B. Security Guard at that time.

September 21, 1974: A sand cave in San Francisco's Hunter's Point, had a cave in. Sadly, one person died and one person was hurt. Shown in the photo is Charlotte Washington, a K.B. Security Guard at that time.

Photo: Clem Albers, San Francisco Chronicle

September 21, 1974: A sand cave in San Francisco's... Photo-12352997.141211 - SFGate

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Taboola Gallery Frame Item-85307.141211 - SFGate

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October 18, 1972: Col. Pierre B. Denson and Officer Richard Wader look at Denson's car, sitting over a sinkhole at Sacramento and Presidio Streets in San Francisco.

October 18, 1972: Col. Pierre B. Denson and Officer Richard Wader look at Denson's car, sitting over a sinkhole at Sacramento and Presidio Streets in San Francisco.

August 24, 1968: The Street that dropped out. This cave in of Eastmoor Avenue in Daly City, just south of San Francisco, severed mains, sent water gushing down a slope causing six families to leave their homes, forced closing of a freeway off-ramp and left someone a big clean up job. Officials were trying to track down rumors saying the cave in was predicted before it happened. They were relying on an investigation that pointed to soil erosion. less

August 24, 1968: The Street that dropped out. This cave in of Eastmoor Avenue in Daly City, just south of San Francisco, severed mains, sent water gushing down a slope causing six families to leave their homes, ... more

Photo: Stan Creighton, San Francisco Chronicle

August 24, 1968: The Street that dropped out. This cave in of... Photo-12353000.141211 - SFGate

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December 17, 1962: A large cave in appeared on Franklin and Green Streets in San Francisco.

December 17, 1962: A large cave in appeared on Franklin and Green Streets in San Francisco.

Photo: Art Frisch, San Francisco Chronicle

December 17, 1962: A large cave in appeared on Franklin and Green... Photo-12353002.141211 - SFGate

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November 30, 1960: A water main break caused the street to collapse along 34th Avenue at Wawona Street in San Francisco.

November 30, 1960: A water main break caused the street to collapse along 34th Avenue at Wawona Street in San Francisco.

Photo: Gordon Peters, San Francisco Chronicle

November 30, 1960: A water main break caused the street to collapse... Photo-12353007.141211 - SFGate

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Taboola Gallery Frame Item-85307.141211 - SFGate

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December 30, 1960: Two workmen were pinned beneath a ton of earth and a huge wooden beam in a Pacific Heights excavation when an embankment collapsed "with a roar like a dynamite blast." Firemen and police officers worked about an hour to dig the two victims free of the 30' beam that pinned them. The workmen, Earl Kelley and Melvin Green suffered leg injuries. The were shoveling dirt in the 15' deep excavation for Sarah Dix Hamlin School on Vallejo Street. less

December 30, 1960: Two workmen were pinned beneath a ton of earth and a huge wooden beam in a Pacific Heights excavation when an embankment collapsed "with a roar like a dynamite blast." Firemen and police ... more

Photo: Bob Campbell, San Francisco Chronicle

December 30, 1960: Two workmen were pinned beneath a ton of earth... Photo-12353008.141211 - SFGate

Archival photos of sinkholes from around the United States. Photo-12363476.141211 - SFGate

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May 11, 1981: Winter Park, FL - A sinkhole which had grown to a diameter of approximately 40' wide and 125' deep swallowed a home, several businesses, a municipal swimming pool, a truck and five Porsches. Photo courtesy of AP. less

May 11, 1981: Winter Park, FL - A sinkhole which had grown to a diameter of approximately 40' wide and 125' deep swallowed a home, several businesses, a municipal swimming pool, a truck and five Porsches. Photo ... more

A large sinkhole formed on Sacramento Street between Lyon and Baker streets in San Francisco on April 21, 2016, after a sewer line broke.

A large sinkhole formed on Sacramento Street between Lyon and Baker streets in San Francisco on April 21, 2016, after a sewer line broke.

Photo: Kale Williams

A large sinkhole formed on Sacramento Street between Lyon and Baker... Photo-9878884.141211 - SFGate

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Taboola Gallery Frame Item-85307.141211 - SFGate

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A sinkhole spanned three lanes of 1st Street near Howard Street in San Francisco on September 13, 2007, after a broken water main undermined the paved street above. Crews were attaching the water connection to a new building on 1st Street when an unknown failure caused the main to rupture. less

A sinkhole spanned three lanes of 1st Street near Howard Street in San Francisco on September 13, 2007, after a broken water main undermined the paved street above. Crews were attaching the water connection to ... more

A large sinkhole formed on Sacramento Street between Lyon and Baker streets in San Francisco on April 21, 2016, after a sewer line broke.

A large sinkhole formed on Sacramento Street between Lyon and Baker streets in San Francisco on April 21, 2016, after a sewer line broke.

Photo: Kale Williams

A large sinkhole formed on Sacramento Street between Lyon and Baker... Photo-9878886.141211 - SFGate

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May 14, 1981: Altamonte, FL - As the drought in the state had continued, another sinkhole appeared in a residential area near Orlando.The hole, which was approximately 50' wide and 40' deep swallowed a fence and garden between two homes and cracks around the edge threatened the houses. Photo courtesy UPI. less

May 14, 1981: Altamonte, FL - As the drought in the state had continued, another sinkhole appeared in a residential area near Orlando.The hole, which was approximately 50' wide and 40' deep swallowed a fence ... more

May 14, 1981: Altamonte, FL - As the drought in the state had... Photo-12353030.141211 - SFGate

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April 11, 1977: Deland, FL - a 60' sinkhole swallowed much of the home of Mr. and Mrs. R.H. Lawson near Deland, taking the two family cars, too. They escaped harm. The retired couple had moved into the new home in January of that year. Photo courtesy of AP. less

April 11, 1977: Deland, FL - a 60' sinkhole swallowed much of the home of Mr. and Mrs. R.H. Lawson near Deland, taking the two family cars, too. They escaped harm. The retired couple had moved into the new home ... more

October 2, 1992: Virginia City, NV - Vehicle belonging to Kay Walker, sits at the bottom of a 40' wide crater left after an old time mine shaft collapsed in Virginia City. No one was injured. The historic mining town sits above a honeycomb of old shafts that date back to the area's gold and silver mining days. Photo courtesy of AP. less

October 2, 1992: Virginia City, NV - Vehicle belonging to Kay Walker, sits at the bottom of a 40' wide crater left after an old time mine shaft collapsed in Virginia City. No one was injured. The historic ... more

June 14, 1993: Atlanta, GA - Police and firefighters secure an area where an enormous sinkhole over a hundred feet in diameter in the parking lot of the Mariott Courtyard Hotel collapsed by a break in a sewer culvert. The collapse, which claimed the life of one person, and one other missing at that time, occurred during heavy rainfall. Photo courtesy of the AP. less

June 14, 1993: Atlanta, GA - Police and firefighters secure an area where an enormous sinkhole over a hundred feet in diameter in the parking lot of the Mariott Courtyard Hotel collapsed by a break in a sewer ... more

May 22, 1982: Scranton, PA - A Wilkes-Barre man disappeared wen a mine shaft caved in swallowing the 35 ton crane working on a mine finishing project. the man, Jerry White, was an electrician. Photo courtesy of AP. less

May 22, 1982: Scranton, PA - A Wilkes-Barre man disappeared wen a mine shaft caved in swallowing the 35 ton crane working on a mine finishing project. the man, Jerry White, was an electrician. Photo courtesy ... more

November 14, 1957: Seattle, WA - A huge hole in a north end Seattle boulevard, caused by a broken main trunk sewer, continued expanding slowly, and threatened to swallow homes. About 50 persons were evacuated shortly before dawn, after the hole grew to about 150' long and 75' wide. Photo courtesy of AP. less

November 14, 1957: Seattle, WA - A huge hole in a north end Seattle boulevard, caused by a broken main trunk sewer, continued expanding slowly, and threatened to swallow homes. About 50 persons were evacuated ... more

November 14, 1957: Seattle, WA - A huge hole in a north end Seattle... Photo-12353043.141211 - SFGate

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July 6, 1982; Gainesville, FL - a 50' sinkhole swallowed a red 1982 Oldsmobile at the Maracaibo Manor Apartments in Gainsville. The 10' by 20' hole was eventually stabilized. Photo courtesy of AP.

July 6, 1982; Gainesville, FL - a 50' sinkhole swallowed a red 1982 Oldsmobile at the Maracaibo Manor Apartments in Gainsville. The 10' by 20' hole was eventually stabilized. Photo courtesy of AP.

August 2, 1959: Philadelphia, PA - Police officer lost in street cave in. Huge, gaping hole in street in north east section of Philadelphia is where a policeman disappeared the night before, where he was investigating the cave in. The area was then evacuated because of the escape of illuminating gas. Photo courtesy of AP. less

August 2, 1959: Philadelphia, PA - Police officer lost in street cave in. Huge, gaping hole in street in north east section of Philadelphia is where a policeman disappeared the night before, where he was ... more

July 18, 1961: Philadelphia, PA - Search for house collapse victims. Firemen and other rescue workers use huge crane and shovel as they continued to search for at least 3 persons who were believed to be buried under debris after a section of Philadelphia row houses collapsed. The house dropped into an underground creek used as a massive sewer. One small child had been found alive more than 3 hours after she was buried that day. Photo courtesy AP. less

July 18, 1961: Philadelphia, PA - Search for house collapse victims. Firemen and other rescue workers use huge crane and shovel as they continued to search for at least 3 persons who were believed to be buried ... more

November 15, 1957: Seattle, WA - A huge crater appeared in the 16th Ave N.E. and Ravenna Boulevard the prior Monday. By this date, it had stopped enlarging. Engineers diverted drains and sewers to prevent further erosion which threatened the residential district. Photo courtesy of Unite Press Telephoto. less

November 15, 1957: Seattle, WA - A huge crater appeared in the 16th Ave N.E. and Ravenna Boulevard the prior Monday. By this date, it had stopped enlarging. Engineers diverted drains and sewers to prevent ... more

November 15, 1957: Seattle, WA - A huge crater appeared in the 16th... Photo-12353050.141211 - SFGate

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July 5, 1960: Chicago, ILL - The sky didn't fall on driver Richard W. Tawlak, but the ground dropped out from under him. He possibly suffered broken ribs when a section of Langley Avenue caved under his car. A witness ran across the street to get a better look and was hit by a car and suffered two broken arms. less

July 5, 1960: Chicago, ILL - The sky didn't fall on driver Richard W. Tawlak, but the ground dropped out from under him. He possibly suffered broken ribs when a section of Langley Avenue caved under his car. ... more

In this image provided by the National Corvette Museum shows several cars that collapsed into a sinkhole Wednesday, Feb. 12, 2014, in Bowling Green, Ky. The museum said a total of eight cars were damaged when a sinkhole opened up early Wednesday morning inside the museum. (AP Photo/National Corvette Museum, HO) less

In this image provided by the National Corvette Museum shows several cars that collapsed into a sinkhole Wednesday, Feb. 12, 2014, in Bowling Green, Ky. The museum said a total of eight cars were damaged when a ... more

In this image provided by the National Corvette Museum shows... Photo-7578855.141211 - SFGate

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A truck hangs over the edge of a sinkhole that opened up in the parking lot of Hughes Relocation Services, Monday, June 25, 2012, in Salt Springs, Fla. Tropical Storm Debby raked the Tampa Bay area with high wind and heavy rain Monday in a drenching that could top 2 feet over the next few days and trigger widespread flooding. (AP Photo/The Ocala Star-Banner, Alan Youngblood) less

A truck hangs over the edge of a sinkhole that opened up in the parking lot of Hughes Relocation Services, Monday, June 25, 2012, in Salt Springs, Fla. Tropical Storm Debby raked the Tampa Bay area with high ... more

Photo: Alan Youngblood, Associated Press

A truck hangs over the edge of a sinkhole that opened up in the... Photo-3122237.141211 - SFGate